Directional radio system



April 5, 1949 y. B. BGNALL 2,466,354

DIRECTINAL RADIO SYSTEM Filed June 28, 1944 Puing eviaes 5 Combining .lpparatus rzte-Ima Element k Patented Apr. 5, 1949 UNITE DmnorioNaL Ramo SYSTEM Application June 2S, 1944-', Serial No. '542,536

8 Claims.

This invention relates to a directional radio system for transmitting and receiving signals,

andparticularlyto one in which a symmetrical 'antenna array'may be steered eiiectiv'ely either in Asteps or continuously to 'obtain maximum directivity in any horizontal direction, and which `isalso'capable of iecting an adjustment of the airc'raft-to-ground services, it is ordinarily practicable to employ antennas of the directive type only at the iixed stations. Owing to the somewhat limited power available on mobile units,

andalso owing to the relatively high noise level on such units, it is desirable that the transmit- A ting and receiving antennas at the fixed stations shall have relatively high gain and also noise discrmination to effect satisfactory transmission with such mobile units. Those require-ments, and

the further requirement of obtaining directivityl in any selected direction in which a mobile unit may be' operating with respect to the fixed station,

necessitates either the provision of a large numberv of 'fixed directive antennas whose directional characteristics are such as to provide a reasonable covera-ge in the Zones in which the mobile units are operating or, on the other hand, means for-'rotating the entire antenna, including its physical supporting structure in order to provide the directional characteristic necessary at a parl ticular instant of time.

Both of those methods are undesirable from the standpoint of cost' and the operating complications that would ensue.

This invention resides in a directional radio systememploying a single antenna array which is capable of being steered eiectively, either in Vsteps or continuously, so as to obtain maximum directivity in any horizontal direction and in which 'the' verticall directive pattern may also be adjusted. This invention is not only applicable to fixed' stations in the mobile radio services where the distance and direction oi transmission vaiy over wide limits, but is also desirable 'for forked radio I'services Where a single transmitter or receiver is employed to operate with a plurality olf other xed stations at various distances and in various directions from the rst mentioned station, and likewise from each other. yA further applicationof" this steerable antenna arrangenientfis that of direction iinding` l points, such as 6.

'e'eowsatm The invention is also applicable for use in connection with the operation of long-haul radio 4circuits on which the Waves are subject to large angular deviation from'a mean value, both in the horizontal and vertical planes. The antenna array employed inthe aforementioned services, might be used-alone or'as an antenna element in a Musa array meaning a multiple unit steerable antenna system which is fully described in the Bell Laboratories Record, vol. XVI, No; 5 (January 1938) pages 148 to 156, and No. 6 (February 1938), pages 203 to 207.

This invention will be fully understood from the following description when read in connec tion with the attached drawing, ci which Figure l shows schematically the embodiment of the invention in its most `general form; llig. 2 shows diagrammatically an arrangement of the phase shifting devices; 3 shows an arrangement in which the steering may be eiiected in smaller steps than in the arrangements previously shown; Fig. e shows the adaptation of the invention to a system employing a plurality of frequencies simultaneously; Fig. 5 shows means to enable the phase shifting' to be done at a lower frequency by employing a modulator and an oscillator to bea-t down the received frequency; and'Fig 46 shows the method of proportioning a receiving or transmitting system in which this inventionis embodied,

The antenna array of Fig. l. comprises'a plurali'ty of identical antenna elements l, 2, 3, etc. arranged in symmetrical form about a center as, for example,V ori-the circumference of a circle and are 'equidistantly spaced thereon. -The antenna element may be of any type having a circularly symmetric horizontal characteristic such as a simple vertical` antenna, multi-element vertical antenna and vertical cage antenna. The

antenna element l is connected by the trans* mission line'A d to the fixed Contact point t of a switch and each of the other antenna elements 2, 3, etc. is 'similarly connected. The transmission lines are preferably, butfn'ot necessarily, oli the `coaxial type and `should be of equalilength; and each line terr'ninates in a contact point, such as 5, which is intended to engage the other contact The Contact point t is connected by the transmission line l to a `phasing andl combining arrangement 8 at the` center 'of the array, the connection including an impedance-matchingdevice 9 to match the impedance l`of the circuits'lookingin both directions from the device 9. Each ofthe other" contacts, sir'nlin `lar 'to ii, is similarlyv connected to the phasing and combining apparatus il, and each connection includes an impedance-matching device similar to 9. The circuits extending from the contacts such as li to the phasing and combining apparatus 8 are xedly mounted upon a disk or turn-table represented symbolically by the dot and dash circle iii, and therefore are moved as a unit Whenever the disk is rotated. In View of the unitary arrangement of the circuits upon the disk It) it is obvious that if the disk is rotated so as to bring the movable contact point 6 into contact with a lixed contact point other than 5, the phasing networks, which form part of the phasing and combining apparatus 8 would be connected in the same relative manner to the antenna elements after rotation of the disk as they were prior to such rotation. This automatically ensures the proper phasing oi the currents from the several antennas to produce an additive effect in the phasing and combining apparatus 3, whenever a change occurs in direction of the wave front of the received waves. The phasing and combining arrangement El is connected by the transmission line li to the radio receiver I2. The manner in which the arrangement shown in Fig. 1 functions in order to accomplish the purpose of the invention is as follows:

Let it be assumed that the position of the Wave front of the approaching wave is as represented by the dot and dash line A--A and is moving in the direction indicated by the arrows. The voltages set up in the antenna elements I, 2, 3, etc. which differ in phase will be transmitted to the phasing and combining apparatus i3 and the resultant voltage will be transmitted over the transmission line H to the receiver l2. In the arrangement shown, the distances from the center of the disk lil to all of the antenna elements are equal, and, as hereinbefore stated, the impedance-matching devices 9 serve to match the impedance looking toward the antenna elements and the impedance looking toward the radio receiver. When the phasing has been once adjusted for a symmetrical antenna array for a particular direction of approach o'i the wave front, as represented by the line AA, the system may be readily adjusted for maximum reception of waves coming from another direction, as represented by the line B-B by merely rotating the disk so as to bring the movable contact point 6 into contact with the xed contact point i3, connected to the antenna element 3. By that operation, the phasing network forming a part of the phasing and combining apparatus il, which formerly was connected by the transmission line 'l to the antenna element l, is, after rotation of the disk, connected by the same transmission line to the antenna element 3 which has the same angular position with respect to the Wave front B--B as antenna element i had With respect to the wave front A-A. In like manner the phasing networks which, prior to rotation of the disk were connected to other antenna elements symmetrically arranged with respect to element l, will, after rotation of the disk, be connected to other antenna elements which have the saine relative positions with respect to element 3. This means that, after rotation of the disk, the phas ing networks will be connected to antenna elements that have the same (or substantially the same) angular position with respect to the latter wave front B-B as they had, prior to rotation, with respect to the lorlncr wave lront AMA. Then the voltage waves set up in the various antenna elements by the waves whose frontis represented by B-B will produce the same additive eiect in phasing and combining arrangement B as when the wave front had the position represented by the line A-A.

Figs. 2 to 6 illustrate various ways in which the phase adjustments may be made and the outputs combined. In Fig. 2, in which the same nu morals have been used to represent parts similar to those shown in Fig. 1, the movable contact point 6 is connected to a combining network 8 by the conductor l, the connection including a phase shifter ifi. Similar phase Shifters are inserted in the connections between the other mov able contact points and the combining network. Each phase shifter has the characteristic necessary to make the total phase delay from each antenna elementequal for a wave arriving in the desired horizontal and vertical directions. The phase Shifters may consist of suitable electrical networks, ror they may be transmission lines having the required lengths to effect the necessary phase delay for the voltage wave of the antenna with which they may be connected, as described in my copending application, Serial No. 542,537, filed Juno 28, 1944, which issued as Patent No. 2,432,134. The use of an actual transmission line as the phase-adjusting device is desirable not only because of simplicity, but also because it possesses the desirable characteristic that the required line length for phase adjustment is independent of the operating frequency, so that, when adjusted for any frequency the phase compensation will be correct for any other frequency. With the arrangement of Fig. 2,

,j steering in the horizontal direction may be accomplished in angular steps by mechanically rotating the xed phase adjusters as a unit with respect to the antenna elements. The directive pattern of the array may be steered horizontally in steps corresponding to the angular separation between the antenna elements through a complete circle of 360 degrees.

The sharpness of the major lobe of the directive characteristic of an antenna of the type contemplated increases as the ratio 0f the array radius to the operating wave-length increases, and also as the number of antenna elements is increased. Thus, 'for a given number of antenna elements the angular width of the major lobe of the directive pattern decreases as the size of the array is increased. If a high degree of directivity is required in the major lobe and is obtained by increasing the size of the array in proportion to the wave-length without increasing the number of elements a point may be reached Where the antenna directivity is too great for the angular steps in which the array is steered thus resulting in substantial decrease in effectiveness of the array at intermediate angles between the angular steps to which the array can be steered. To compensate for this variation in effective gain versus angle between steps. intermediate phase-adjusting networks Ilia-Md may be used as indicated in Fig. 3. In, this manner and by proper choice of array size and number of elements: any required degree of uniformity in gain over a required angular range can be obtained for arrays having any required maximum directivity. With the arrangement shown in Fig. 3 the outputs from each group of phase shiiters are combined through amplifiers I6 as indicated, thus isolating each group ci phase slliltcrs.

In the aforedescribed arrangement the vertical plane characteristic of the directive pattern ofl 1the-array is iixed with reference to the horizontalfplane characteristic by the design and adjustment of the phasing arrangement therein shown. However, in the manner similar to that shown in 3 intermediate or auxiliary phaseadjusting networks may be provided to steer the directive characteristics in the vertical plane in steps: as desired. In that manner the array-may becontrollably steered in nite steps over the full'- range of horizontal and vertical angles of 360, degrees and 90 degrees, respectively.

Fig.' 4 shows in simplified form an arrangement by which the directional characteristics may be adjusted-for each of a plurality of frequencies. In- :this 4arrangement the transmission line is connected to a plurality of amplifiers il', the output of-'each olf which is connected to a lter such as I8." The iilters are in turn connected to a xed'contact point 5 of switching contacts. The movable contact points are connected through the-phase-shifters it -to the bus-bars iii, which bus-bars are connected through the ampliiiers Zitto the line il Aleading to the radio receiver i2. The phased'outp-uts of the phase Shifters It are combined after passing through the ampliers 2i! and the combined results are impressed upon the-radio receiver.

Fig. 5 shows'a form of invention in which the received frequencyl is beaten down to a lower frequency before being impressed upon the phase shiftingnetwork. In that figure the antenna element l, one of a plurality of similar elements, is connected by the transmission line t to the input side of the modulator 2i. The beating frequency is supplied to the modulator 2i by the oscillator 2li-over 'a circuitv that includes conductor H, ampliiier 22, phase shifter 9, terminals 5'andtof the switch and the modulator 2i. rlihe lower'frequency, lresulting from the beating operation, passes to the output of the modulator 2| which is connected by conductors 26 and 2l to the amplifier 2d, which is in turn connected to the Iline il extending to the radio receiver l2. Other antenna elements would be connected to the junction point by a circuit similar to that by which the antenna element i is so connected. The voltage Wave, set up in the antenna elements such as l, would be impressed upon the modulator 2i upon which are also impressed oscillations of the beating frequency transmitted iro-rn the oscillator 23 over the line Il and through the amplii-ler 2?., the phase shifter 9 and the terminals 5 and 6 of the switching contact. intermediate frequency will be impressed lupon the input side of the am-pliier 2d, together with the currents of the same intermediate frequency from other modulatorsv connected to other antenna elements similar to I. The combined currents, as amplified by 2li, would then be transmitted over the line Ii to the radio receiver l2 wherein they would be detected by oscillations of the frequency ofthe oscillator 23. In the arrangement shown in Fig. 5, the phase shifter Q acts upon the beating r,frequency of the oscillator 23,- and thus controls the phase relationship of thecutput currents of the plurality of modulators, each of which is individual to an antenna element. By reversing the vterminals of the ampliiiers 22 and 2d; and likewise reversing the connection ofthose ampliiiers to the input and theV output terminals of the modulator il, the beating frequency would then be conveyed from the oscillator 23 over a path that includes the linefl I, amplifier 2t, the input terminals of the modulatorf k2 l and the outputfoi Ethat i modulator The resultant wouldl be transmitted to the lradio receiverv l2' over a path-that includes the phase shifter 9,:

the amplifier and the line il. In the latter arrangement the shiit vof phase is made upon the modulated output current instead of upon the current of the beating frequency, lfrom the oscillator' 2?, as occurs with the amplifiers arranged as shown in Fig. 5.

The directional characteristic of an array, the .magnitude of the output current and the necessary phase adjustment may be determined in the vfollowing manner:

ln Fig. 6 one form oi antenna array of the type contemplated having symmetry about a centrai point is shown diagrammatically. In this array N antenna elements are arranged with equal spacing on the circumference of a circle having a radius R. If the center of the array is considered as the reference point for phases and the outputs from the separate antenna elements are combined in parallel after transmission through lines of equal length R or equal phase shift the output current at the angular frequency w corresponding to the wave-length A can be represented by the expression N ZA k6 I=K sin w15 (l) for an impressed piane Wave as indicated in Fig. 6. r'he notation in. the above and following equations is as follows:

From the geometry of Fig. 6 the following relation holds:

Using this relation and Equation l the combined output current of the array is N I=K sin wt ZAM;

To make all elements add in phase for =B and =zi artincial phase shift may be added to each branch in the amount 2l qSk=;-R[llcos (dk-ell) cos A] (5) or the phase shift may be added by prcviding additionaltransmission line of the appropriate length. in `each branch oi `the' array at'apoint A i www 7 ahead of the combining junction. The required line length is given by where V/Vo is the ratio of phase velocity in the transmission line to the velocity of light. It should be noted that the length of line required in each branch is independent of the frequency.

With these phase adjustments the output current may be represented by I=K sin wt AkeJfjuk (7) k=1 where uk=7rR [cos (0k-B) cos A-cos (0k-) cos (8) Equation '7 can be reduced to the form I=K sin wt N 2 N 2 EAI, cos uk) -i-(ZAI, sin uk) Then for this special case Equation 9 reduces to lll' I=K sin wt 2214 cos uk (10) Equation l0, t'.o ;'cther with Equation 8 gives the complete directional characteristics of a circular array consisting of M doublets phased to obtain maximum directivity in the direction Although this invention has been described in connection with its function to receive radio Waves for subsequent impression upon a radio re ceiver, it is to be understood that such descrip tion is purely illustrative of the structure and the mode of functioning of the invention, but does not constitute a limitation upon it since it is equally applical'ile for use in connection with a radio transmitter. The sole change necessary to effect such a diierence in functioning would be merely an interchange of the connections of the apparatus to provide for the diiference in direction of flow of the currents between the elements of the antenna array and the translating device, that is, a radio receiver or radio transmitter.

While this invention has been disclosed as embodied in particular forms and arrangements of parts, it is not so limited since it is capable of embodiment in other and different forms without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a directional radio system, the combination with a plurality of antennas spaced equidistantly apart upon the circumference of a circle, of a translating device intended for simultaneous connection to all of the said antennas. means to connect the said device to all of the said antennas, the said connecting means including phase-shifting means adjusted to bring into phase the currents from all antennas, and means operable at will, to simultaneously rotate all of the said connecting means and establish a connection between said translating device and the antennas of the said array to automatically adjust the said system for optimum reception for diierent angles of approach of the Wave front.

2. In a directional radio system, the combination with an antenna array comprising a plurality of antennas spaced equidistantly apart upon the circumference of a circle, of a radio transmitter or receiver intended for connection to all of the said antennas and means to connect the said transmitter or receiver to the said antennas, the said connecting means -comprising a plurality of branches each being designed to automatically eiect the necessary phase adjustment of the voltage Waves set up in its branch to ensure the optimum transmission -or reception of the radio Waves transmitted or received by the said antenna array.

3. In a directional radio system, the combination with an antenna array comprising a plurality of antennas spaced equidistantly apart upon the circumference of a circule, of a radio translating device and a plurality of means to simultaneously couple the said device to all antennas of the said antenna array, each of said coupling means being designed and proportioned to effect such phase adjustment of the voltage Wave being conducted thereover, that the combined effect upon the said translating device of all such voltage Waves Afrom all of the said antennas shall be a maximum for radio Waves impressed upon the said array from any given direction, and means to simultaneously rotate all of said coupling means whenever the wave front of the radio Waves approaches the array from a different direction whereby each of said means will connect said device with another of said antennas, thereby automatically adjusting the said system for maximum eiect regardless of the direction of approach of the said radio waves.

4. In a directional radio system, the combination with a plurality of antennas spaced equidistantly apart upon the circumference of a circle, a translating device intended for simultaneous `connection to all of the said antennas, means comprising a plurality of branches to connect the said device to all of the said antennas for the transmission of radio Waves therefrom, each branch of the said connecting means in cluding phase-shifting means to adjust the phase of the currents set up in the antennas so that the radiations therefrom will produce a cumulative eifect in a given direction, and means t0 simultaneously rotate all of the branches of the said connecting means and establish a diierent connection between said translating device and the antennas of the said array in order to automatically adjust the said system for optimum reception or transmission for different angles of approach of the Wave front.

5. In a directional radio system, the combination with an antenna array comprising a plurality of antennas spaced equidistantly apart upon the circumference of a circle, of a radio transmitting device and a plurality of means to couple the said device to the said antenna array, each of said coupling means being designed and proportioned to eilect such phase adjustment of the voltage wave being conducted thereover, that the eiect of all such voltage waves upon their respective antennas shall be such as to produce maximum radiation in any given direction, and means to simultaneously rotate all of said coupling means and to connect each of them to another of said antennas without changing the sequence of the said connections, thereby automatically adjusting the said system for maximum effect regardless of the direction of transmission of the said radio waves.

6. In a directional radio system, the combination with an antenna array comprising a plurality of antennas of a radio receiver, means to couple the said receiver to the said array, the said coupling means comprising a combining network and a plurality of phase controlling circuits each extending from the said network to one of said antennas, each of said circuits having a switching contact to eiiect connection to an antenna and also means to adjust the phase of the voltage Wave set up in each circuit by the antenna to which the said circuit may then be connected so that the voltage Waves in all of said circuits will produce the maximum effect in the combining network when the wave-front of the radio waves makes a given angle with a given axis of the antenna array, and means to simultaneously rotate all of the said phase controlling circuits so as to connect each such circuit to another antenna to automatically produce maximum reception for a diierent angle of wavefront of the radio waves.

7. In a directional radio system, the combination with a circular antenna array comprising a plurality of antennas of a radio receiver, means to couple the said receiver to each of said antennas, the said coupling means comprising a combining network and a plurality of phase controlling circuits each connecting 'the said network to one of said antennas, the said circuits being so adjusted as to produce the maximum effect in the combining networkfor a radio wave approaching the said array from a given direction, and means to simultaneously rotate all of the said phase controlling circuits and to connect each to another antenna without altering the sequence of the said phase controlling circuits, thereby ensuring maximum receptivity for a radio Wave approaching the said array from another direction.

8. In a directional radio system the combination with an antenna array comprising a plurality of pairs of antennas arranged oppositely and symmetrically about a central point, means to apply current to all of the pairs of the said antennas, the said means being adapted to control the phase and amplitude of the currents in the several antennas whereby the directional characteristic may be controlled, and means to alter at will the said characteristic by simultaneously changing the connections of the said means to the said antennas, in accordance with a fixed plan.

VERNON B. BAGNALL.

REFERENCES CITED The following references are of record in the file of this patent:

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